I said 3. Over the course of time, I prefer a campaign world in which many parties can act, many adventures can take place, and many plots can be ongoing. I like to offer plenty of neat places to explore that have little or nothing to do with anyone's ongoing plot....and even plot-based locations should exhibit some sense of history and other useage.
In terms of plots, I have no "DM plots" per se. What I have is "NPC plots". One NPC, for example, wants to take over the area the PCs are in and make it a "New Parthelonian Empire". This plot is ongoing until it is resolved (through PC action or not), and crops up sometimes in unrelated adventures. Similarly, the aboleth in the sewers under Selby-by-the-Water have been working toward collapsing the town for nearly a century now. One of the three aboleth was destroyed by NPCs before the game started, one was destroyed by PCs in-game, and one still exists.
Whenever possible, I try to tie PC backstory into the history of the area and the ongoing NPC plots. Some examples:
1. One PC decided to go the "I have total amnesia" route, and made his character left-handed. I decided to rule that he was the escaped reflection of a powerful wizard. The players loved this!
2. One PC (Hrum, see my main story hour) was a half-orc and left his family tree blank. I decided to rule that he was descended from a rape when the town of Oakhille was looted by orcs. This gave him ties to an adventure area and gave him an opportunity to meet the ghost of his grandmother's lover. Unfortunately, he died before that could happen. These sorts of tie-ins do not give you plot immunity.
3. Another PC decided that his parents were friends of the deceased wizard/greenbond Amoreth the Arcane, and that his parents had deserted him when he was very young. Since Amoreth the Arcane had died stopping the first of the three aboleth beneath Selby-by-the-Water, I decided that the PC's parents must have been involved in this. They didn't desert thier child; they died trying to make his home secure.
So, there are a lot of things to give players direction
if they need it, but nothing to force them in a single direction. No one -- PC or NPC -- is immune from death simply because they tie into an ongoing plot, and as plots belong to the NPCs (not the DM) they may be smashed well before they come to fruition.
As an example of this last: When the Bonewardens sought to use a drug to increase hostilities between men and orcs, the group followed the early leads, tracked the villains down, and defeated them before even finding out exactly what the plot was.
I enjoy folklore, and seed areas with bits of folk stories and fairy tales that the PCs might become part of. When the PCs found a dead girl in the sewers, one of them returned the body to her parents. As a result, she was buried, and her spirit helped to avert that PC's death later (Motif: The Grateful Dead).
Finally, I also like to play with recurrences. Old enemies (defeated but not slain) return (possibly as allies), NPCs met might be met again, lost treasures may be found, old adventuring areas are re-entered, and (best of all) seemingly insignificant events are discovered to have more importance as time goes on.
I listed this as a "3" out of "10". YMMV.
RC